Three pyramids in one: Mayan Kukulkan pyramid is an architectural "Russian nesting doll"

Once, twice, three times a pyramid: thanks to non-invasive scanning, archaeologists have determined that "El Castilo," also known as the Kukulkan pyramid in Chichen Itza, has two other pyramids inside of it. As The Guardian explains:

"A 10-metre-tall pyramid was found within another 20-metre structure, which itself is enveloped by the 30-metre exterior visible at the Maya archeological complex known as Chichen Itza in Yucatán state. The smallest pyramid was built between the years 550 and 800, engineers and anthropologists said. The middle structure had already been discovered in the 1930s and dates back to the years 800-1000, while the largest one was finished between 1050 and 1300."